Synthesis gas, which is also known as syngas, is a mixture of gases comprising carbon monoxide (CO) and hydrogen (H2). Generally, syngas may be produced from any carbonaceous material. In particular, biomass such as agricultural wastes, forest products, grasses, and other cellulosic material may be converted to syngas.
Syngas is a platform intermediate in the chemical and biorefining industries and has a vast number of uses. Syngas can be converted into alkanes, olefins, oxygenates, and alcohols such as ethanol. These chemicals can be blended into, or used directly as, diesel fuel, gasoline, and other liquid fuels. Syngas can also be directly combusted to produce heat and power. The substitution of alcohols and/or derivatives of alcohols in place of petroleum-based fuels and fuel additives can be particularly environmentally friendly when the alcohols are produced from feed materials other than fossil fuels.
Gasoline is a refined petroleum product which is burned in the engines powering most of the world's automobiles. Petroleum is a non-renewable resource of finite supply. Acute shortages and dramatic price increases in petroleum and the refined products derived from petroleum have occurred, particularly during the past several decades. Extensive research is now being directed toward replacing a portion of petroleum-based gasoline with a cleaner-burning fuel derived from a renewable resource, such as biomass in a biorefinery.
In recent years, considerable research has been devoted to providing alternative sources and manufacturing routes for liquid hydrocarbon fuels in recognition of the fact that petroleum is a non-renewable resource and that petroleum-based fuels such as gasoline and distillate will ultimately become more expensive.
A major development within the chemical/petroleum industry has been the discovery of the special catalytic capabilities of a family of zeolite catalyst based upon medium-pore size shape selective metallosilicates. Discoveries have been made leading to a series of analogous processes drawn from the catalytic capability of zeolites. Depending upon various conditions of space velocity, temperature, and pressure, methanol can be converted in the presence of zeolite-type catalysts to olefins which can oligomerize to provide gasoline or distillate, or can be converted further to produce aromatics.
It has been demonstrated that alcohols, ethers, and carbonyl-containing compounds can be converted to higher hydrocarbons, particularly aromatics-rich high-octane gasoline, by catalytic conversion employing a shape-selective medium pore acidic zeolite catalyst such as H-ZSM-5. This conversion is described in, among others, U.S. Pat. Nos. 3,894,103; 3,894,104; 3,894,106; 3,907,915; 3,911,041; 3,928,483; and, 3,969,426. The conversion of methanol to gasoline in accordance with this technology (the “MTG” process) produces mainly C5+ gasoline-range hydrocarbon products together with C3-C4 gases and C9 heavy aromatics. The desirable C6-C8 aromatics (principally benzene, toluene and xylenes) can be recovered as a separate product slate by conventional distillation and extraction techniques.
Traditional approaches for converting syngas to gasoline involve a two-step process comprising converting syngas to methanol followed by converting methanol to gasoline. What are needed, in view of the art and commercial drivers, are process configurations, apparatus, and suitable catalysts for conversion of syngas into gasoline components as well as oxygenates, such as alcohols, for blending into oxygenated gasoline. Additionally, methods that proceed through higher alcohols (ethanol and heavier) are desired in order to take advantage of the state of the art for ethanol synthesis and higher-alcohol synthesis from syngas.